[zh] Sync changes from English site (5)
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Qiming Teng
@@ -42,8 +42,7 @@ considered implementation details and are subject to change without warning.
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For more up-to-date specification, see
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[Kubernetes DNS-Based Service Discovery](https://github.com/kubernetes/dns/blob/master/docs/specification.md).
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-->
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## 怎样获取 DNS 名字?
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## 哪些对象会有 DNS 名字? {#what-things-get-dns-names}
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在集群中定义的每个 Service（包括 DNS 服务器自身）都会被指派一个 DNS 名称。
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默认，一个客户端 Pod 的 DNS 搜索列表将包含该 Pod 自己的名字空间和集群默认域。
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@@ -74,7 +73,6 @@ Services, this resolves to the set of IPs of the pods selected by the Service.
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Clients are expected to consume the set or else use standard round-robin
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selection from the set.
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-->
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### 服务 {#services}
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#### A/AAAA 记录
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@@ -117,17 +115,35 @@ Kubernetes 会为命名端口创建 SRV 记录，这些端口是普通服务或
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<!--
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### A/AAAA records
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Any pods created by a Deployment or DaemonSet have the following
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DNS resolution available:
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In general a pod has the following DNS resolution:
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`pod-ip-address.deployment-name.my-namespace.svc.cluster-domain.example.`
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`pod-ip-address.my-namespace.pod.cluster-domain.example`.
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For example, if a pod in the `default` namespace has the IP address 172.17.0.3,
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and the domain name for your cluster is `cluster.local`, then the Pod has a DNS name:
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`172-17-0-3.default.pod.cluster.local`.
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Any pods created by a Deployment or DaemonSet exposed by a Service have the
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following DNS resolution available:
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`pod-ip-address.deployment-name.my-namespace.svc.cluster-domain.example`.
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-->
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### A/AAAA 记录
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经由 Deployment 或者 DaemonSet 所创建的所有 Pods 都会有如下 DNS
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解析项与之对应：
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一般而言，Pod 会对应如下 DNS 名字解析：
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`pod-ip-address.deployment-name.my-namespace.svc.cluster-domain.example.`
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`pod-ip-address.my-namespace.pod.cluster-domain.example`
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例如，对于一个位于 `default` 名字空间，IP 地址为 172.17.0.3 的 Pod，
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如果集群的域名为 `cluster.local`，则 Pod 会对应 DNS 名称：
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`172-17-0-3.default.pod.cluster.local`.
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Deployment 或通过 Service 暴露出来的 DaemonSet 所创建的 Pod 会有如下 DNS
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解析名称可用：
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`pod-ip-address.deployment-name.my-namespace.svc.cluster-domain.example`.
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<!--
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### Pod's hostname and subdomain fields
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@@ -146,7 +162,6 @@ domain name (FQDN) "`foo.bar.my-namespace.svc.cluster-domain.example`".
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Example:
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-->
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### Pod 的 hostname 和 subdomain 字段
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当前，创建 Pod 时其主机名取自 Pod 的 `metadata.name` 值。
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@@ -254,6 +269,51 @@ record unless `publishNotReadyAddresses=True` is set on the Service.
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才会有与之对应的记录。
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{{< /note >}}
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<!--
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### Pod's setHostnameAsFQDN field {#pod-sethostnameasfqdn-field}
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-->
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### Pod 的 setHostnameAsFQDN 字段 {#pod-sethostnameasfqdn-field}
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{{< feature-state for_k8s_version="v1.19" state="alpha" >}}
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<!--
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**Prerequisites**: The `SetHostnameAsFQDN` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/)
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The `SetHostnameAsFQDN` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/)
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must be enabled for the
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{{< glossary_tooltip text="API Server" term_id="kube-apiserver" >}}
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When a Pod is configured to have fully qualified domain name (FQDN), its hostname is the short hostname. For example, if you have a Pod with the fully qualified domain name `busybox-1.default-subdomain.my-namespace.svc.cluster-domain.example`, then by default the `hostname` command inside that Pod returns `busybox-1` and the `hostname -fqdn` command returns the FQDN.
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-->
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**前置条件**：`SetHostnameAsFQDN`
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[特性门控](/zh/docs/reference/command-line-tools-reference/feature-gates/)
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必须在 {{< glossary_tooltip text="API 服务器" term_id="kube-apiserver" >}}
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上启用。
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当你在 Pod 规约中设置了 `setHostnameAsFQDN: true` 时，kubelet 会将 Pod
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的全限定域名（FQDN）作为该 Pod 的主机名记录到 Pod 所在名字空间。
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在这种情况下，`hostname` 和 `hostname --fqdn` 都会返回 Pod 的全限定域名。
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{{< note >}}
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<!--
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In Linux, the hostname field of the kernel (the `nodename` field of `struct utsname`) is limited to 64 characters.
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If a Pod enables this feature and its FQDN is longer than 64 character, it will fail to start. The Pod will remain in `Pending` status (`ContainerCreating` as seen by `kubectl`) generating error events, such as Failed to construct FQDN from pod hostname and cluster domain, FQDN `long-FQDN` is too long (64 characters is the max, 70 characters requested). One way of improving user experience for this scenario is to create an [admission webhook controller](/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks) to control FQDN size when users create top level objects, for example, Deployment.
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-->
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在 Linux 中，内核的主机名字段（`struct utsname` 的 `nodename` 字段）限定
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最多 64 个字符。
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如果 Pod 启用这一特性，而其 FQDN 超出 64 字符，Pod 的启动会失败。
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Pod 会一直出于 `Pending` 状态（通过 `kubectl` 所看到的 `ContainerCreating`），
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并产生错误事件，例如
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"Failed to construct FQDN from pod hostname and cluster domain, FQDN
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`long-FQDN` is too long (64 characters is the max, 70 characters requested)."
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（无法基于 Pod 主机名和集群域名构造 FQDN，FQDN `long-FQDN` 过长，至多 64
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字符，请求字符数为 70）。
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对于这种场景而言，改善用户体验的一种方式是创建一个
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[准入 Webhook 控制器](/zh/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks)，
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在用户创建顶层对象（如 Deployment）的时候控制 FQDN 的长度。
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{{< /note >}}
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<!--
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### Pod's DNS Policy
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@@ -278,10 +338,15 @@ following pod-specific DNS policies. These policies are specified in the
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`dnsConfig` field in the Pod Spec.
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See [Pod's DNS config](#pod-s-dns-config) subsection below.
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-->
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### Pod 的 DNS 策略 {#pod-s-dns-policy}
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- "`Default`": Pod 从运行所在的节点继承名称解析配置。
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参考[相关讨论](/zh/docs/tasks/administer-cluster/dns-custom-nameservers/#inheriting-dns-from-the-node) 获取更多信息。
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- "`ClusterFirst`": 与配置的集群域后缀不匹配的任何 DNS 查询（例如 “www.kubernetes.io”）
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DNS 策略可以逐个 Pod 来设定。目前 Kubernetes 支持以下特定 Pod 的 DNS 策略。
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这些策略可以在 Pod 规约中的 `dnsPolicy` 字段设置：
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- "`Default`": Pod 从运行所在的节点继承名称解析配置。参考
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[相关讨论](/zh/docs/tasks/administer-cluster/dns-custom-nameservers/#inheriting-dns-from-the-node)
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获取更多信息。
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- "`ClusterFirst`": 与配置的集群域后缀不匹配的任何 DNS 查询（例如 "www.kubernetes.io"）
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都将转发到从节点继承的上游名称服务器。集群管理员可能配置了额外的存根域和上游 DNS 服务器。
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参阅[相关讨论](/zh/docs/tasks/administer-cluster/dns-custom-nameservers/#impacts-on-pods)
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了解在这些场景中如何处理 DNS 查询的信息。
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@@ -293,10 +358,10 @@ following pod-specific DNS policies. These policies are specified in the
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<!--
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"Default" is not the default DNS policy. If `dnsPolicy` is not
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explicitly specified, then “ClusterFirst” is used.
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explicitly specified, then "ClusterFirst" is used.
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-->
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{{< note >}}
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"`Default`" 不是默认的 DNS 策略。如果未明确指定 `dnsPolicy`，则使用 "`ClusterFirst`"。
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"Default" 不是默认的 DNS 策略。如果未明确指定 `dnsPolicy`，则使用 "ClusterFirst"。
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{{< /note >}}
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<!--
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